A structure is described in FIG. 2 of WO01/036235, in which a retractor is arranged on a vehicle floor and the end of an inflatable lap belt is retracted around the retractor. In this conventional example, an inflator is arranged on the vehicle floor and gas is introduced to the lap belt via a special structure called a plenum.
[Patent Document 1] WO01/036235
In the above-mentioned WO01/036235, the special member called the plenum is used so as to have a complicated structure and high cost. The plenum is also bulky and the degree of freedom in arrangement is low.